Apparatus and methods for introducing anesthesia to the spinal column have been available for many years. The majority of these methods and apparatus introduce anesthesia either by an epidural procedure, whereby the anesthesia is inserted into the epidural space via an epidural needle and catheter combination; or by a spinal procedure whereby the anesthesia is inserted through the dura itself into the subarachnoid space via a spinal needle.
An example of the epidural procedure is described in U.S. Pat. No. 4,349,023 to Gross. In this procedure, a sharp pointed hollow epidural needle is used to pierce the skin and spinal ligaments into the epidural space located between the ligaments and the dura. Catheter tubing is inserted through the lumen of the needle. The needle is removed and a syringe containing anesthesia is coupled to the distal end of the catheter. Anesthesia is provided to the patient via the syringe and catheter as needed throughout the medical procedure. This procedure allows the use of a relative large and steady epidural needle to insert the catheter. However, since the fluid is inserted into the epidural space, rather than directly into the subarachnoid space, the reaction time is relatively slow. Therefore, the procedure must be initiated a relatively long time before commencing surgery to ensure that the patient is sufficiently anesthetized. One advantage, however, of this procedure is that the precise amount of anesthesia necessary for the intended medical procedure, need not be determined, since the syringe or other device for storing the anesthesia may be replenished and thus administered continuously during the medical procedure.
The second common procedure for administering anesthesia is through a spinal needle, an example of which is described in U.S. Pat. No. 4,518,383 to Evans. In this procedure, a sharp pointed outer needle is pushed through the patient's skin and ligaments until it reaches the epidural space, stopping well before the dura wall to prevent damage thereto. A sharp pointed spinal needle is then inserted within the outer needle until it pierces the dura wall. A syringe containing anesthesia is coupled to the base of the spinal needle and anesthesia is transmitted from the syringe, though the spinal needle, directly into the dura. While this procedure is both simple and quick, it has been known to create what is referred to in the art as "spinal headache" a condition which results when punctures are made in the dura wall. It is believed that by reducing the size of the puncture made in the dura wall, the incidence of spinal headache may also be reduced. Thus, attempts have been made to reduce the gauge of the spinal needle, to thereby reduce the size of the puncture (gauge is measured by the outer diameter of the needle). However, as the needle gauge is reduced, the needle becomes so flexible and fragile that proper placement of the needle is extremely difficult. Moreover, since this procedure provides a "one shot" administration, that is, the needle is inserted and removed after the anesthesia is administered, the particular dosage of anesthesia required must be accurately determined before administration. Therefore, if the medical procedure continues for longer than that which was initially anticipated, it is possible that a second difficult insertion would have to be made in order to administer additional anesthesia. Such a result will significantly disrupt the medical procedure.
Recently, attempts have been made to combine the spinal and epidural procedures to provide both a controlled injection of anesthesia via a catheter, as well as to eliminate the incident of spinal headache by reducing the gauge of the instrument used to penetrate the dura and to administer the anesthesia. One example is described in U.S. Pat. No. 3,780,733 to Martinez-Manzor. This procedure provides a relatively large needle (15 gauge) for reaching the epidural space. A smaller gauge catheter with a 25 gauge needle on its end is inserted through the larger needle until it punctures the dura wall. A syringe containing anesthesia is connected to the distal end of the catheter. Anesthesia is then introduced directly into the dura through the catheter. One major problem with this procedure is that it is not suitable for use with very small gauge catheters, e.g., 28 gauge. This is because when unsupported, such fine gauge catheters are highly subject to breaking when the requisite amount of force required to puncture the dura is applied thereto. Furthermore, without guidance, it is very difficult to maneuver such fine gauge catheters within the body. Thus, it is extremely difficult to ensure proper placement.
To further minimize the incidence of spinal headache, it has also been proposed to insert a very small gauge catheter, typically a 32-gauge catheter, into the dura through a larger 26-gauge standard spinal needle which is used to puncture the dura. One problem with this procedure is that it creates a hole in the dura wall which is larger than the diameter of the catheter, thus minimizing the opportunity of a seal to be created between the catheter and the dura wall, and allowing the incidence of cerebral spinal fluid (CSF) leakage. Furthermore, while the incidence of spinal headache may be reduced by this procedure, it is not likely eliminated, since a 26-gauge needle is still of sufficient diameter to cause such. Moreover, a small 32-gauge catheter is extremely fragile and placement of the same has proven difficult at best. In addition, the lumen of this catheter is so small that it is easily susceptible to kinking which makes it impossible to transport anesthesia through the catheter. Thus, this method suffers from not only the problem of spinal headache, but also of difficult placement within the dura, resulting in a substantially unreliable procedure.